Windowed thermal ablation probe

ABSTRACT

This invention relates to an electrosurgical device having a hollow shaft, an electrically conductive distal tip that is also adapted for penetrating bone, and an intermediate electrically insulating spacer.

RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. 10/259,689 , filed Sep. 30, 2002, entitled “Novel Device for Advancing a Functional Element Through Tissue”, the specification of which is incorporated by reference.

BACKGROUND OF THE INVENTION

In an effort to reduce back pain through early intervention techniques, some investigators have focused upon nerves contained within the vertebral bodies.

For example, PCT Patent Publication No. WO 01/0157655 (“Heggeness”) discloses ablating nerves contained within the vertebral body by first boring into the vertebral body with a nerve ablation device, placing the tip of the device in close proximity to the nerve, and then ablating the nerves with the tip. Heggeness discloses numerous devices, such as electricity transmitting probes, as candidate nerve ablation devices. In describing how to use such as probe, Heggeness discloses “raising the temperature of tip 24 such that the intraosseous nerve is ablated by the heat generated by electrical current passing through tip.” See Heggeness at page 8, line 28. The probe disclosed by Heggeness appears to be a solid metal rod functioning as the active electrode of a monopolar Rf device.

U.S. Pat. No. 6,478,793 (“Cosman”) discloses ablative treatment of metastatic bone tumors, including those within the spine. Pain relief is reportedly achieved by penetrating the bone wall with a suitable probe, and applying heat through the probe to ablate either the bone tumor or the tissue near the bone tumor. Cosman teaches the use of both monopolar and bipolar probes in this application. See Cosman at col. 5, line 44. Cosman also teaches that the treatment may also be used to ablate the nerves and nerve ramifications in and/or around the bone to desensitize them against further tumor encroachment. See Cosman at col. 8, line 50–65, and col. 9, lines 9–17.

The only probes specifically disclosed by Cosman appear to be monopolar. However, monopolar approaches require the use of a grounding pad beneath the patient and allows energy to flow from the probe and to dissipate in the surrounding tissue. Because the path by which the energy flows from a monopolar probe to its corresponding pad is uncontrolled, the energy may undesirably flow through sensitive tissue, such as the spinal cord. Since this method may cause undesired local muscle or nerve stimulation, it may be difficult or dangerous to operate in sensitive areas of the human body.

Cosman teaches that the electrode may be rigid and robust and capable of piercing bone. Cosman teaches that the electrode may comprise a metal tubular shaft (with appropriate wall thickness to prevent buckling or bending during penetration of hard bone) with a rugged pointed tip. See Cosman at col. 6, lines 34–46. Beyond teaching the use of a generic bipolar probe, Cosman does not disclose any particular bipolar electrode configuration.

U.S. Pat. No. 6,168,593 (“Sharkey”) discloses thermal probes in which the electrodes are disposed at an angle to the longitudinal axis of the probe. In one embodiment, an electrode is located in a laterally—disposed window of a tubular, electrically insulating shaft. See FIG. 1A. According to Sharkey, this electrode can ablate tissue at an angle to the principal axis of the probe.

Although the probe disclosed in FIG. 1A of Sharkey appears to be monopolar, Sharkey also teaches that “bipolar delivery can be implemented using the techniques of the current invention by providing at least two distinct elements on the tip, each connected to outgoing and return electrical paths from the RF power supply.

Sharkey does not disclose a return and an active electrode located within the same window. Sharkey does not disclose a window in a conductive shaft. Sharkey does not disclose a probe having a tip adapted to penetrate bone.

U.S. Pat. No. 5,944,715 (“Goble”) discloses electrosurgical instruments wherein active electrodes 14 are housed within a window of an insulator. See FIGS. 1 and 4.

Like Sharkey, Goble does not disclose a return and an active electrode located within the same window, nor a window in a conductive shaft, nor a probe having a tip adapted to penetrate bone.

SUMMARY OF THE INVENTION

The present inventors have found that the shaft of a bipolar probe adapted to penetrate bone can be made by simply joining a solid, sharp tip onto a hollow tube. The resulting shaft is of sufficient strength to penetrate the cortical shell of a vertebral body. Furthermore, since the shaft comprises a hollow tube, wires for an electrode can be housed within the tube, thereby allowing a bipolar or sesquipolar configuration. The combination of the ability to penetrate a cortical shell and the ability to provide bipolar or sesquipolar function represents an advance over the conventional technology.

Therefore, in accordance with the present invention, there is provided an electrosurgical device, comprising:

-   -   a) a hollow shaft having an annular wall having a longitudinal         bore therein, a proximal portion and a distal portion, and a         first window extending transversely through the annular wall,         and     -   b) a first electrode disposed within the window and being in         electrical connection with a power supply, and     -   c) a tip having a proximal end portion, a sharp tipped distal         end adapted to penetrate cortical bone, the proximal end portion         of the tip mechanically connected to the distal portion of the         bore of the hollow shaft.

In some embodiments, a space is provided between the tip and tube for ease of manufacturing.

Also in accordance with the present invention, there is provided an electrosurgical device, comprising:

-   -   a) a hollow shaft having an annular wall having a longitudinal         bore therein, a proximal portion and a distal portion, and     -   b) an electrically insulating spacer having a proximal end and a         distal end portion, the proximal end being mechanically         connected to the distal portion of the bore of the hollow shaft.

In another aspect of the present invention, the present inventors have found that if the tubular portion of the shaft is made of an electrically conductive material and a window is formed in that tubular portion, then a simple and effective probe can be made by electrically insulating the rim of the window and then placing an electrode within the insulated window. This configuration allows the construction of a bipolar electrode having a simple and low cost design.

Therefore, in accordance with the present invention, there is provided an electrosurgical device, comprising:

-   -   a) a hollow shaft having an annular wall having a longitudinal         bore therein, a proximal portion and a distal portion, and a         first window extending transversely through the annular wall and         defining an inside rim, and     -   b) a first electrode disposed within the window and being in         electrical connection with a power supply, and     -   c) an electrically insulating material disposed between the         inside rim of the first window and the first electrode.

Also in accordance with the present invention, there is provided an electrosurgical device, comprising:

-   -   a) a hollow shaft made,of an electrically conductive material         having an annular wall having a longitudinal bore therein, a         proximal portion and a distal portion, and a first window         extending transversely through the annular wall, and     -   b) a first electrode disposed within the window and being in         electrical connection with a power supply.

In some embodiments, both the return and active electrodes are housed within the same window, thereby further reducing the complexity of the manufacturing process.

Therefore, in accordance with the present invention, there is provided an electrosurgical device, comprising:

-   -   a) a hollow shaft having an annular wall having a longitudinal         bore therein, a proximal portion and a distal portion, and a         first window extending transversely through the annular wall,         and     -   b) an active electrode disposed within the window and being in         electrical connection with a power supply, and

a return electrode disposed within the window and being in electrical connection with the power supply.

DESCRIPTION OF THE FIGURES

FIG. 1 discloses a side view of a device of the present invention having a pair of complimenary electrodes housed within a window and electrically isolated from the inside rim of the window by an insulating material.

FIG. 2 discloses a side view of a device of the present invention having a single electrode housed within a window and electrically isolated from the inside rim of the window by an insulating material.

FIG. 3 discloses a side view of a device of the present invention having a pair of electrodes traversing the diameter of the shaft and housed within opposing windows.

FIG. 4 discloses a side view of the present invention having a plurality of electrodes housed within a plurality of windows.

FIG. 5 a discloses a side view of a device of the present invention in which the device has been longitudinally cross-sectioned to reveal nesting features.

FIG. 5 b discloses an exploded view of FIG. 5 a.

FIG. 6 discloses a cross-sectional view of a device of the present invention having a grooved distal tip and a crimped shaft.

FIG. 7 discloses a cross-sectional view of a device of the present invention having a throughhole traversing the distal tip and shaft and filled with a bonding material.

FIGS. 8 a and 8 b disclose distal tips of the present invention having chamfered features.

FIGS. 9 a–f disclose acircular transverse cross sections of the sharp tip.

FIG. 10 discloses a device of the present invention having a means for delivering fluid that delivers fluid through an opening on the surface of the distal tip.

FIG. 11 discloses a device of the present invention having a means for delivering fluid that delivers fluid through an opening on the surface of the insulating spacer.

FIG. 12 a discloses a device of the present invention having a means for delivering fluid that delivers fluid through a plurality of openings on the surface of the insulating spacer

FIG. 12 b discloses a transverse cross section of FIG. 12 a, taken through the spacer.

FIGS. 13 a–b are cross-sections of devices of the present invention having slidable temperature probes.

FIG. 13 c is a cross-section depicting various preferred locations for a temperature probe of a device of the present invention.

FIG. 14 a–b are cross-sections of devices of the present invention having multi-sensor temperature probes.

FIG. 15 a is a cross-section of a device of the present invention having radially segmented electrodes.

FIG. 15 b is a side view of a device of the present invention having axially segmented electrodes.

FIG. 16 is a side view of a device of the present invention having slidable electrodes.

FIG. 17 is a side view of a device of the present invention in which both the tip and shaft of the device are return electrodes.

FIGS. 18 a and 18 b present axial and transverse cross-sectional views of an embodiment of the present invention in which the electrode surfaces are configured to allow current to flow out of only one side of the device.

FIGS. 19 a and 19 b present axial cross-sectional views of a telescoping embodiment of the present invention in which the electrodes are in respective undeployed and deployed configurations.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of the present invention, the “resistive heating zone” is the zone of bone tissue that is resistively heated due to an energy loss incurred by current traveling directly through the bone tissue. Resistive heating, “joule” heating and “near-field” heating may be used interchangeably herein. The “conductive heating zone” is the zone of bone tissue that is heated due to the conduction of heat from an adjacent resistive heating zone. The total heating zone (“THZ”) in a bone tissue includes both the resistive heating zone and the conductive heating zone. The border between the conductive and resistive heating zones is defined by the locations where the strength of the electric field is 10% of the maximum strength of the electric field between the electrodes. For the purposes of the present invention, the heating zones encompass the volume of bone tissue heated to at least 42° C. by the present invention. For the purposes of the present invention, the “first and second sides” of a vertebral body are the lateral-lateral sides intersected by the basivertebral nerve (“BVN”).

Preferably, the present invention comprises a novel probe adapted for piercing cortical bone and having a novel bipolar electrode configuration. More preferably, the present invention comprises a sharp stainless steel tip of sufficient sharpness to pierce cortical bone that is welded to one end of a hollow stainless steel shaft (or, “hypotube”). More preferably, a slot or window is cut into the distal portion of the shaft, thereby providing a window into which insulated electrodes can be placed. The insulation of the electrodes can be accomplished by providing an insulating material, such as a plastic insert or a potted encapsulant, between the inner rim of the window and the electrode.

This design is advantageous over conventional designs because it provides a relatively inexpensive device that is sufficiently rigid and strong to pierce cortical bone, thereby allowing its use for treating osseous nerves and bone tumors within the bone.

In some embodiments, the outer metal shaft of the inventive probe can be coated with an electrical insulator, such as PTFE to electrically insulate the shaft from the body tissue.

In another embodiment of the present invention, there is provided a radiofrequency (RF) applicator device (or “probe”) comprising a hollow rigid tube (such as stainless steel) fitted with a handle at its proximal end and an insulating spacer at its distal end, wherein a portion of the insulating spacer is nested within the distal end of the hollow tube. The proximal end of a distally disposed sharp tip is then nested through the spacer and into the distal end of the hollow tube, thereby imparting electrical isolation and greater strength to the assembled device. Preferably, the hollow tube is adapted to be a first electrode and the tip is adapted to be a second electrode, thereby forming a bipolar heating device adapted for treating hard tissue. Preferably, the device may optionally include channels or ports through which a conductive fluid, such as saline, can be delivered to the heating zone to improve the efficiency of the device.

Now referring to FIG. 1, there is provided an electrosurgical device 1, comprising:

-   -   a) a hollow shaft 3 having an annular wall having a longitudinal         bore therein, a proximal portion 9 and a distal portion 11, and         a first window extending transversely through the annular wall         and forming a rim 15, and     -   b) an active electrode 21 disposed within the window and being         in electrical connection with a power supply via first lead 23,     -   c) a return electrode 31 disposed within the window and being in         electrical connection with the power supply via second lead 33,     -   d) an electrically insulating material 61 disposed between the         inside rim of the window and the first electrode,     -   e) a tip 51 having a solid proximal end 53 and a sharp tipped         distal end 55 adapted to penetrate cortical bone, the proximal         end of the tip being mechanically connected to the distal         portion of the bore of the hollow shaft,     -   f) an outer insulating shell 71 surrounding the proximal portion         of the hollow shaft,     -   g) a thermocouple 81 disposed within the electrically insulating         material and being in electrical connection with a digital         thermometer via third pair of leads 83.

The shaft of the present invention preferably comprises a hollow tube that allows at least one lead wire to be run therethrough. The material selection and dimensions of the shaft should be selected so as to allow the shaft to support the penentration of the cortical bone by the tip without yielding. Typically, the shaft is made of a metallic or ceramic material. Preferably, the shaft is made of a conductive material, such as a metal. Preferably, the metallic shaft material is selected from the group consisting of stainless steel, titanium, titanium-containing alloys, such as nitinol, copper, and copper plated with gold or platinum. More preferably, the metallic shaft material is stainless steel. In some embodiments, the shaft has a length of between 3 and 20 cm (preferably between 5 cm and 12 cm, an inner diameter of between 0.5 and 5 mm (preferably between 5 and 3 mm), and an outer diameter of between 1 and 6 mm (preferably between 2.0 and 4 mm). When the dimensions of the shaft are within these ranges, conventional biomaterials such as stainless steel can be suitably used.

In some embodiments, the proximal end of the spacer is received over the distal end of the shaft.

The function of the electrodes of the present invention is to be in direct contact with tissue and provide a pathway for RF current through a portion of the tissue surrounding the probe, thereby therapeutically heating the tissue. The electrodes are typically made of metals, such as stainless steel, platinum, gold, copper (nickel-plated or gold-plated), platinum, or a conductive polymer (such as a carbon- or silver-filled epoxy). Preferably, the electrode material of construction is such that its coefficient of thermal expansion is within 50% of the coefficient of thermal expansion of the material selected as the insulator 61.

The function of the insulating annulus of the present invention is to electrically insulate the electrodes located within the window from the electrically conductive shaft. The insulating annulus is typically made of PTFE, nylon, an epoxy, a polyurethane, a polyimide, or other suitable polymer, or a ceramic material.

Preferably, tip 51 provides two functions. First, its sharp tipped distal end 55 should be sufficiently pointed to penetrate cortical bone. Accordingly, although angle α may be any angle between about 0 degrees and about 90 degrees, angle α is preferably between 20 and 70 degrees. When the tip angle is below this range, the tip may be fragile and may be susceptible to breaking during cortical rim penetration. When the angle is above this range, the tip is too blunt and may require excessive force to achieve cortical rim penetration. In some embodiments, the proximal portion of the tip is solid, thereby providing additional strength to the tip. In some embodiments, the proximal portion of the tip has a diameter that substantially the same as the outer diameter of the shaft. In this condition, the proximal portion of the tip may be mechanically joined to the distal end of the shaft (for example, by welding) to produce a strong, streamlined probe.

In other embodiments, the sharp tipped distal end is formed near the axial center of the tip to produce a conical shape.

In some embodiments, the device further comprises an outer insulating sleeve (such as sleeve 71) surrounding at least the proximal portion of the hollow shaft. The function of the sleeve is to electrically isolate the device from the tissue that is adjacent the target tissue, thereby increasing the safety and effectiveness of the device. In some embodiments, the material of construction for the sleeve is selected from the group consisting of polymeric materials such as PTFE and ceramic materials such as alumina. In some embodiments, the sleeve is provided in the form of a coating upon the shaft. In other embodiments, the sleeve is manufactured separately and slid over the shaft. Typically, the sleeve has a length that is between 50% and 95% of the length of the shaft length. In some embodiments, the sleeve extends distally towards the window and terminates within one length of the window.

In some embodiments, the thermocouple is coupled to the power supply in a feedback loop to modulate the power output and thereby control the temperature at the tip.

Now referring to FIG. 2, in other embodiments, the device of FIG. 1 could be modified so that shaft window 213 houses only a single electrode 221. In this instance, the conductive shaft could be electrically connected to the power supply via a handle (not shown) to become the second electrode 223 of a bipolar design. The advantage of having only a single electrode within the window is that the area of the window can be decreased, thereby enhancing the strength of the shaft. When only a single electrode is located within the window, the surface area of that electrode is generally between 0.5 and 20 mm². This is advantageous in applications requiring relatively larger surface area electrodes. In such embodiments, this embodiment can capably accommodate the larger surface area electrode without increasing window area. In some embodiments, the single windowed electrode could be the active electrode, while in others it could be the return electrode. In some embodiments, the single windowed electrode is the active and has a surface area of between 0.5 and 20 mm².

In this configuration, the placement of an insulating sleeve preferably provides a distal uninsulated portion of the shaft having a length of between 3 mm and 20 mm, and is more preferably about 5 mm. In preferred embodiments thereof, the insulation is selected from the group consisting of polyimide tape, PTFE tape, and heat shrink tubing. One preferred thickness of the insulation ranges from about 0.006 mm to about 0.012 mm) (i.e., about 0.00025 to 0.0005 inches), and is provided by a dielectric coating, such as a polyimide coating.

Now referring to FIG. 3, in other embodiments, the device of FIG. 1 could be modified to include a pair of windows 313,315 located on opposite sides of the shaft. In such an embodiment, the electrodes 321,323 and insulator 361 could be modified to essentially traverse the bore and connect the windows. This embodiment advantageously allows the clinician to treat target zones on either side of the device, and so is advantageous in instances in which the device is placed within a target tissue such as a tumor.

Alternatively, in some embodiments, neither electrode completely traverses the transverse width of the tube. In some embodiments thereof, each electrode opens through a window on the same side of the tube. In other embodiments thereof, a first electrode opens through a first window on a first side of the tube, and a second electrode opens through a second window on a second side of the tube, preferably on a diametrically opposed side of the tube.

Now referring to FIG. 4, in other embodiments, the device of FIG. 1 could be modified to include a plurality of windows 413, 415, 417 spaced along the length of the shaft, wherein each window has at least one electrode 423, 425, 427 located therein. Each of these windows is electrically isolated from the conductive shaft by an insulating annulus 461, 463, 465. The provision of multiple windowed electrodes allows the surgeon the ability to either treat different zones at different times without needing to move the device, or to treat a larger area. In some embodiments having a series of windows (not shown), both the return and active electrodes can be located within the same window. In other embodiments, each window houses a single (preferably, active) electrode, and the second (preferably, return) electrode 433,435,437 is provided on the surface of the electrically conductive shaft between bands of insulating material. In other embodiments, the second return electrode is provided by another windowed electrode. Thus, the surgeon can select any pair of electrode to define the treatment area. In this particular embodiment, return electrode 433 is electrically connected to the power supply via an internal lead (not shown) and is electrically isolated from the remainder of the shaft by insulating windows comprising left side portion 491 and right side portion 493.

In some embodiments, and now referring to FIG. 5 a and 5 b, an intermediate spacer 591 is provided between the shaft 511 and the sharp tip 521. When this spacer is made of an electrically insulating material, the sharp tip 521 could be adapted to function as the first electrode. In some embodiments thereof, the shaft 511 could be adapted to function as the second electrode. The use of the tip and shaft as paired electrodes is advantageous because of its simplicity of design and assembly, and its larger active surface area.

In some embodiments, as in FIGS. 5 a and 5 b, the insulating spacer is hollow. The hollow nature of the spacer allows a lead wire to run therethrough and electrically connect the sharp tip to the power supply, and also allows the proximal end 523 of the tip to be nested in the hollow distal portion 595 of the spacer. In these FIGS. 5 a and 5 b, the proximal end portion 593 of the hollow spacer is nested within the distal end portion 513 of the conductive shaft.

The robust nature of the embodiment shown in FIG. 5 a could be further enhanced by proximally extending the nested portion of the hollow spacer sufficiently deep into the distal portion of the shaft, thereby providing increased surface area for bonding.

Similarly, the proximal end portion 523 of the sharp tip (the distal half 525 of which is preferably solid) can be made to extend so far proximally as to nest in the conductive shaft. Because the intervening spacer is made of an electrically insulating material, the conductive tip is electrically isolated from the conductive shaft. The proximal extension of the tip into the shaft likewise increases the robust nature of the probe.

Now referring to FIG. 6, the robust nature of the probe could be further fortified to prevent tip pull-out by providing a circumferential groove 601 in the nested portion of the solid tip and providing a swage or crimp 603 in the portion of the outer shaft overlying the groove. In such embodiments, the intervening insulating spacer should be made of a material sufficiently malleable to accept crimping or swaging.

Now referring to FIG. 7, the robust nature of the probe could be further fortified to prevent tip pull-out by providing a transverse through-hole 701 through the probe in the area of the nested portion of the solid tip and then filling the throughhole with a bonding material such as an adhesive such as epoxy, or with an electrically non-conductive locking pin or screw.

Now referring to FIG. 8 a, in some embodiments, it may be desirable to provide a tapered feature 801 upon the distal end of the sharp tip. Providing such a tapered feature is advantageous because a) it will prevent the device from penetrating through the anterior cortical wall of the vertebral body, and b) it will reduce current density at the electrode tip and minimize regions of excessive current density, thereby providing an even heating zone. In some embodiments, as in FIG. 8 a, the tapered feature comprises a chamfer. In others, as in FIG. 8 b, the tapered feature is more substantial and preferably comprises an essentially 180 degree rounded curve, such as a semicircle or a bullet nose 803.

Now referring to FIGS. 9 a–9 f, in some embodiments, the transverse cross section of the sharp tip is acircular. The acircular cross section may allow the clinician to generate differently shaped heating profiles, or to access different anatomies (such as between tissue planes, or to follow specific tissue contours (i.e., between the intervertebral disc and spinal cord). In some preferred embodiments, the acircular cross section is selected from the group consisting of rounded (as in FIG. 9 a), oval (as in FIG. 9 b), elliptical (as in FIG. 9 c), bilobular (as in FIG. 9 d), arc-like (as in FIG. 9 e) and s-shaped (as in FIG. 9 f).

If the active electrode has no active cooling means, it may become be subject to conductive heating induced by the heated tissue, and the resultant increased temperature at the electrode-tissue interface in the electrode may adversely affect performance by charring the adjacent bone tissue. Accordingly, in some embodiments, a cool tip active electrode may be employed. The cooled electrode helps maintain the temperature of the electrode at a desired temperature. Cooled tip active electrodes are known in the art. Alternatively, the power supply may be designed to provided a pulsed energy input. It has been found that pulsing the current favorably allows heat to dissipate from the electrode tip, and so the active electrode stays relatively cooler.

In some embodiments, and now referring to FIG. 10, it may also be desirable to provide a means for delivering a fluid to the distal end of the device. The fluid may be a cooling fluid that will help control the heating activity, or it may be a carrier for therapeutic agents such as drugs, or provide an electrolyte solution (such as isotonic or hypertonic saline) for efficient current flow. In some embodiments, providing the means for delivering a fluid could be accomplished by providing a longitudinal fluid delivery tube 1001 extending from the tubular portion of the shaft to the outer surface 1003 of either the sharp tip 1005 or insulating spacer 1007. Preferably, the fluid delivery tube has a proximal portion 1011 extending into the tubular portion of the shaft and a distal portion 1013 opening onto the outer surface 1015 of the sharp distal tip.

In some embodiments, as in FIG. 10, the fluid delivery tube is provided as a separate physical entity. In other embodiments, the fluid delivery tube is made by simply providing longitudinal, fluidly connected holes in the other components.

Now referring to FIG. 11, in some embodiments in which the sharp tip 1113 also acts as an electrode, the fluid delivery tube 1101 has a proximal portion 1103 extending into the tubular portion 1105 of the shaft and a distal opening portion 1109 opening onto the outer surface 1111 of the insulating spacer. In these embodiments, the spacer acts not only as a conduit for fluid delivery, it still provides electrical insulation between the sharp tip electrode and the shaft-based electrode. In some embodiments, as in FIG. 11, the fluid delivery tube can comprise a separate physical entity portion 1115 and a portion 1117 produced by making a hole in an already existing component (such as spacer 1121).

Now referring to FIG. 12 a, in some embodiments, multiple fluid delivery tubes 1201, 1203 are used. In these embodiments, conductive efficiency is enhanced because the multiple fluid delivery tubes may now deliver fluid all about the radius of the device, as shown in cross-sectional FIG. 12 b. FIG. 12 b is a cross section of FIG. 12 a taken transversely through the spacer. In FIG. 12 b, longitudinal hole portions 1251 are provided between the inner 1253 and outer 1255 diameters of the spacer to deliver fluid from within the shaft, while radially extending hole portions 1257 extend radially from the longitudinal hole portions and deliver fluid to the outer surface 1259 of the spacer 1261.

In some embodiments, thermocouples are placed in radially extending hole portions of the fluid delivery tubes in order to monitor the surface temperature of the device at various radial locations. In these embodiments, the fluid delivery tube having a thermocouple therein is effectively blocked so that each tube has either a thermocouple or fluid delivery function, but not both.

Also as shown in this embodiment, the proximal portion 1211 of each fluid delivery tube can comprise a single inner wall 1213 and a single outer wall 1215 defining a single large diameter annulus 1217 therebetween. Fluid is delivered through this annulus to the proximal portion 1219 of the plurality of holes 1221 provided in the insulating spacer.

The annular nature of the proximal portion of the fluid delivery tube is also advantageous because it also provides a convenient inner tube 1223 through which a lead 1225 can be run to electrically connect the sharp tip 1227 to the power supply.

In general, it is desirable to operate the present invention in a manner that produces a peak temperature in the target tissue of between about 80° C. and 100° C. When the peak temperature is below 80° C., the off-peak temperatures may quickly fall below about 45° C. When the peak temperature is above about 100° C., the bone tissue exposed to that peak temperature may experience necrosis and charring. This charring reduces the electrical conductivity of the charred tissue, thereby making it more difficult to pass RF current through the target tissue beyond the char and to resistively heat the target tissue beyond the char. In some embodiments, the peak temperature is preferably between 90° C. and 98° C.

It is desirable to heat the volume of target tissue to a minimum temperature of at least 42° C. When the tissue experiences a temperature above 42° C., nerves within the target tissue may be desirably, damaged. However, it is believed that denervation is a function of the total quantum of energy delivered to the target tissue, i.e., both exposure temperature and exposure time determine the total dose of energy delivered. Accordingly, if the temperature of the target tissue reaches only about 42° C., then it is believed that the exposure time of the volume of target tissue to that temperature should be at least about 30 minutes and preferably at least 60 minutes in order to deliver the dose of energy believed necessary to denervate the nerves within the target tissue.

Preferably, it is desirable to heat the volume of target tissue to a minimum temperature of at least 50° C. If the temperature of the target tissue reaches about 50° C., then it is believed that the exposure time of the volume of target tissue to that temperature need only be in the range of about 2 minutes to 10 minutes to achieve denervation.

More preferably, it is desirable to heat the volume of target tissue to a minimum temperature of at least 60° C. If the temperature of the target tissue reaches about 60° C., then it is believed that the exposure time of the volume of target tissue to that temperature need only be in the range of about 0.5 minutes to 3 minutes to achieve denervation, preferably 1 minute to 2 minutes.

Typically, the period of time that an intraosseous nerve (“ION”) is exposed to therapeutic temperatures is in general related to the length of time in which the electrodes are at the target temperature following heat up. However, since it has been observed that the total heating zone remains relatively hot even after power has been turned off (and the electric field eliminated), the exposure time can include a period of time in which current is not running through the electrodes.

In some embodiments, it is desirable to heat the target tissue so that at least about 1 cm³ of bone tissue experiences the minimum temperature. This volume corresponds to a sphere having a radius of about 0.6 cm. Alternatively stated, it is desirable to heat the target tissue so the minimum temperature is achieved by every portion of the bone within 0.6 cm of the point experiencing the peak temperature.

More preferably, it is desirable to heat the target tissue so that at least about 3 cm³ of bone experiences the minimum temperature. This volume corresponds to a sphere having a radius of about 1 cm.

In one preferred embodiment, the present invention provides a steady-state heated zone having a peak temperature of between 80° C. and 100° C. (and preferably between 90° C. and 98° C.), and heats at least 1 cm³ of bone (and preferably at least 3 cm³ of bone) to a temperature of at least 50° C. (and preferably at least 60° C.).

As noted above, a peak temperature below about 100° C. is desirable in order to prevent charring of the adjacent tissue, steam formation and tissue popping. In some embodiments, this is accomplished by providing the power supply with a feedback means that allows the peak temperature within the heating zone to be maintained at a desired target temperature, such as 90–98° C. In some embodiments, between about 10 watts and 30 watts of power is first supplied to the device in order to rapidly heat the relatively cool bone, with maximum amperage being obtained within about 10–15 seconds. As the bone is further heated to the target temperature, the feedback means gradually reduces the power input to the device to between about 6–10 watts.

Although preferred embodiments of the present invention typically comprises bipolar electrodes, the probes of the present invention can be easily adapted to provide monopolar use. For example, the device of FIG. 2 could be modified so that the shaft is electrically isolated at the handle, and a ground electrode is provided to extend from the power supply to the patient.

The following section relates to the general structure of preferred energy devices in accordance with the present invention:

The apparatus according to the present invention comprises an electrosurgical probe having a shaft with a proximal end, a distal end, and at least one active electrode at or near the distal end. A connector is provided at or near the proximal end of the shaft for electrically coupling the active electrode to a high frequency voltage source. In some embodiments, a return electrode coupled to the voltage source is spaced a sufficient distance from the active electrode to substantially avoid or minimize current shorting therebetween. The return electrode may be provided integral with the shaft of the probe or it may be separate from the shaft

In preferred embodiments, the electrosurgical device will comprise a shaft or a handpiece having a proximal end and a distal end which supports one or more electrodes. The shaft may assume a wide variety of configurations, with the primary purpose being to mechanically support the active electrode and permit the treating physician to manipulate the electrode from a proximal end of the shaft. The shaft may be rigid or flexible, with flexible shafts optionally being combined with a generally rigid external tube for mechanical support. Flexible shafts may be combined with pull wires, shape memory actuators, and other known mechanisms for effecting selective deflection of the distal end of the shaft to facilitate positioning of the electrode array. The shaft may include a plurality of wires or other conductive elements running axially therethrough to permit connection of the electrode array to a connector at the proximal end of the shaft.

In some embodiments, the shaft comprises a hollow annulus adapted to be introduced through a posterior percutaneous penetration in the patient. Thus, the shaft adapted for posterior percutaneous use may have a length in the range of about 3 to 25 cm (preferably, 12–15 cm), and a diameter in the range of about 1 mm to about 6 mm (preferably, 2–5 mm). However, for endoscopic procedures within the spine, the shaft will have a suitable diameter and length to allow the surgeon to reach the target site (e.g., a disc) by delivering the shaft through the thoracic cavity, the abdomen or the like. Thus, the shaft may have a length in the range of about 5.0 to 30.0 cm, and a diameter in the range of about 1 mm to about 6 mm (preferably, about 2 mm to about 4 mm). In any of these embodiments, the shaft may also be introduced through rigid or flexible endoscopes.

The probe further comprises one or more active electrode(s) for applying electrical energy to the cancellous region of the vertebral body. The probe may be bipolar and include one or more return electrode(s). In some embodiments thereof, the bipolar probe has an active electrode array disposed at its distal end. In other embodiments, the probe may be monopolar, whereby the return electrode may be positioned on the patient's back, as a dispersive pad. In either embodiment, sufficient electrical energy is applied through the probe to the active electrode(s) to heat the tissue in the target area and thereby denervate at least a portion of the basivertebral nerve within the vertebral body.

In some embodiments, the probe that is delivered percutaneously and/or endoluminally into the patient by insertion through a conventional or specialized guide catheter. The catheter shaft may include a guide wire for guiding the catheter to the target site, or the catheter may comprise a steerable guide catheter. The catheter may also include a substantially rigid distal end portion to increase the torque control of the distal end portion as the catheter is advanced further into the patient's body.

In some embodiments, the electrically conductive wires may run freely inside the catheter bore in an unconstrained made, or within multiple lumens within the catheter bore.

In some embodiments, the tip region of the device may comprise many independent electrode terminals designed to deliver electrical energy in the vicinity of the tip. The selective application of electrical energy is achieved by connecting each individual electrode terminal and the return electrode to a power source having independently controlled or current limited channels. The return electrode(s) may comprise a single tubular member of conductive material proximal to the electrode array. Alternatively, the instrument may comprise an array of return electrodes at the distal tip of the instrument (together with the active electrodes) to maintain the electric current at the tip. The application of high frequency voltage between the return electrode(s) and the electrode array results in the generation of high electric field intensities at the distal tips of the electrode terminals with conduction of high frequency current from each individual electrode terminal to the return electrode. The current flow from each individual electrode terminal to the return electrode(s) is controlled by either active or passive means, or a combination thereof, to deliver electrical energy to the surrounding conductive fluid while minimizing energy delivery to surrounding (non-target) tissue.

In some embodiments, the device further comprises at least one temperature probe. The temperature is preferably selected from the group consisting of a thermocouple, a thermistor, and a fiber-optic probe (and is preferably a thermocouple). Thermocouples associated with the device may preferably be disposed on or within the electrode carrier; between the electrodes (preferred in bipolar embodiments); or within the electrodes (preferred for monopolar embodiments). In some embodiments wherein the electrodes are placed on either side of the basivertebral nerve, a thermocouple is disposed between the electrodes or in the electrodes. In alternate embodiments, the deployable portion of the thermocouple comprises a memory metal.

One common characteristic of conventional thermal therapy devices is the dimensionally fixed nature of the temperature probe. Because of this fixed nature, the temperature probe can not be moved relative to the shaft, and so can not provide spatially-changing analysis unless the shaft is moved as well. Because it is often problematic to move the shaft, the fixed nature of the probe limits the extent of temperature analysis.

Now referring to FIG. 13 a, in one aspect of the present invention, there is provided a thermal therapy device 1301 having a sliding temperature probe. An axial bore 1303 is provided in the shaft 1306 of the present invention, and an elongate carrier 1305 having a probe 1307 disposed thereon is placed within the bore for slidable movement within the bore. Because the carrier is slidable, the temperature probe may be moved to different axial locations along the axis of the shaft by simply pushing or pulling the proximal end portion 1321 of the carrier, thereby providing the clinician with the ability to easily measure temperature at any selected axial location. In this particular instance, the distal end of the shaft has an opening 1311, thereby allowing the probe to record temperatures outside of the shaft.

Therefore, in accordance with the present invention, there is provided a thermal therapy device comprising:

-   -   a) a hollow shaft having an annular wall having an outer surface         and a longitudinal bore therein, the longitudinal bore being in         communication with an opening upon the outer surface,     -   b) a first electrode disposed on or within the shaft and being         in electrical connection with a power supply, and     -   c) a thermal probe having a elongate carrier and a thermal         sensor disposed on the carrier, wherein the carrier is slidably         disposed within the longitudinal bore.

Although the device of FIG. 13 a is useful in providing temperature information along the shaft axis, it can not provide off-axis information. Accordingly, in one preferred embodiment of the slidable probe, and now referring to FIG. 13 b, the carrier 1311 is made of a memory metal material. As before, an axial bore is provided in the proximal portion of the shaft. However, in this embodiment, while the proximal portion 1313 of the bore is linear, the distal portion 1315 of the bore curves to open onto the surface of the shaft through opening 1317, thereby providing a curved bore. An elongate carrier 1311 made of a memory metal having a probe 1319 disposed thereon is placed within the bore for slidable movement within the bore. Because the carrier is made of a memory metal, the temperature probe may be moved to different off-axis locations by simply pushing or pulling the proximal end portion 1321 of the carrier, thereby providing the clinician with an even greater ability measure temperature radially around the device. In some embodiments, the temperature probe 1319 of FIG. 13 b is located at the edge of the target zone to insure that the targeted zone is sufficiently dosed.

The temperature probe shown in FIG. 13 a is located along the central axis of the shaft of the device. Although this central axial location provides ease of manufacture, the ability of the probe to record the actual tissue temperature may be diminished due to the fact that the probe is not actually in the tissue, but rather in he center of the therapeutic device.

Therefore, is some embodiments of the present invention, there is provided a thermal therapy device 1331 having an axially-offset temperature probe. Now referring to FIG. 13 c, there are provided i) a first temperature probe A located within the central axis of the shaft; ii) a second temperature probe B located within the outer wall of the shaft; iii) a third temperature probe C located on the outer surface of the wall of the shaft (i.e., at the wall/tissue interface); and iv) a fourth temperature probe D located on the outer surface of the wall and at the electrode/insulator interface.

Locating the probe a position A allows the device to be easily manufactured. Locating temperature probe B located within the outer wall of the shaft allows the device to be easily manufactured and durable, and avoids biocompatibility issues. Locating third temperature probe C at the wall/tissue interface provides the most realistic estimate of the tissue temperature. Locating fourth temperature probe D at the electrode/insulator interface allows the device to be easily manufactured a provides measurement of a relatively hot region.

In general, bipolar and monopolar electrodes are used to apply a thermal therapy to tissue for a therapeutic effect. Many probes are actively temperature controlled to monitor and apply a certain thermal dose. Also, electrodes are often cooled (internally) to prevent charring near or on the probe tip and thus allow more power to hear tissue further away from the tip and to create a larger treatment zone. One major drawback to this type of device is that the system is not able monitor the temperature of the lesion. It only monitors the tip temperature, which is being cooled to 0° C., to allow more power to be put into the tissue and create a larger lesion.

In one embodiment of the present invention, and now referring to FIG. 14 a, there is provided a thermal therapy device 1401 having a multi-sensor temperature probe comprising a carrier 1403 and a plurality of temperature sensors 1405, 1407 that deploys into the tissue to monitor heating and thermal dose directly distal of the tip. In some embodiments, a sensor 1409 is also provided on the carrier to monitor temperatures in the vicinity of the electrodes 1411. In use, once the device is placed in the tissue, the linear multisensor temperature probe is deployed away from the surface of the probe. Preferably, adjacent multisensors such as 1405 and 1407 are placed about 5 mm apart from each other to give adequate data for temperature distribution within the tissue.

Now referring to FIG. 14 b, there is provided a multisensor temperature probe as in FIG. 14 a, but the carrier is made of a memory metal, thereby allowing the carrier to deploy from a side wall of the shaft and allowing the clincian to record off-axis temperature data simultaneously from sensors 1415, 1417, 1419 and 1421 at a plurality of different locations.

The electrode terminal(s) are preferably supported within or by an insulating support positioned near the distal end of the device. The return electrode(s) may be located on the instrument shaft, on another instrument, or on the external surface of the patient (i.e., a dispersive pad). The return electrode is preferably integrated with the shaft. The proximal end of the shaft preferably includes the appropriate electrical connections for coupling the return electrode(s) and the electrode terminal(s) to a high frequency power supply, such as an electrosurgical generator.

In some embodiments, the distal end of the device has surface geometries shaped to promote the electric field intensity and associated current density along the leading edges of the electrodes. Suitable surface geometries may be obtained by creating electrode shapes that include preferential sharp edges, indented grooves, or by creating asperities or other surface roughness on the active surface(s) of the electrodes. Surface shapes according to the present invention can include the use of formed wire (e.g., by drawing round wire through a shaping die) to form electrodes with a variety of cross-sectional shapes, such as square, rectangular, L or V shaped, or the like. Edges may also be created by removing a portion of the elongate metal shaft to reshape the cross-section. For example, material can be ground along the length of a round or hollow shaft electrode to form D or C shaped electrodes, respectively, with edges facing in the cutting direction. Alternatively, material can be removed at closely spaced intervals along the shaft length to form transverse grooves, slots, threads or the like along the electrodes. In other embodiments, the shaft can be sectored so that a given circumference comprises an electrode region and an inactive region. In some embodiments, the inactive region is masked.

The return electrode is preferably spaced proximally from the active electrode(s) a suitable distance. In most of the embodiments described herein, the distal edge of the exposed surface of the return electrode is spaced about 2 to 25 mm from the proximal edge of the exposed surface of the active electrode(s). This distance may vary with different voltage ranges, the electrode geometry and depend on the proximity of tissue structures to active and return electrodes. The return electrode will typically have an exposed length in the range of about 1 to 20 mm. Preferably, the ratio of the exposed length of the return electrode to the active length of the active electrode is at least 2:1.

The present invention may use a single active electrode terminal or an array of electrode terminals spaced around the distal surface of the shaft. In the latter embodiment, the electrode array usually includes a plurality of independently current-limited and/or power-controlled electrode terminals to apply electrical energy selectively to the target tissue while limiting the unwanted application of electrical energy to the surrounding tissue and environment resulting from power dissipation into surrounding electrically conductive fluids, such as blood, normal saline, and the like. The electrode terminals may be independently current-limited by isolating the terminals from each other and connecting each terminal to a separate power source that is isolated from the other electrode terminals. Alternatively, the electrode terminals may be connected to each other at either the proximal or distal ends of the shaft to form a single wire that couples to a power source. Alternatively, different electrode terminals can be selected to be active, thereby modifying the path of current and subsequent lesion size and location.

In some embodiments, the plurality of active electrodes are radially staggered about the cross-section of the shaft. In some embodiments, the radially staggered electrodes are individually controllable.

Now referring to FIGS. 15 a, there is provided a transverse cross-sectional view of a device of the present invention having a preferred active electrode configuration. This configuration alternates the active electrodes 1501, 1507, 1513, 1515 between insulating elements 1505, 1511, 1509, 1503. The electrodes could be connected such that 1513 was active and the grouping of 1515, 1507 and 1501 was connected to the return of the RF source. This would influence the heating pattern as shown in FIG. 15 a. Other modes of operation would be to connect 1513 to active and 1501 to return, or 1513 and 1501 to active and 1507 and 1515 to ground. Any of several connections will allow for slight changes in the heating pattern HP. In addition, the active electrodes could be multiplexed in time such that 1513 and 1501 would be connected to active and return, respectively for 1 to 10 seconds and then 1515 and 1507 would be connected to active and return for 1 to 10 seconds. In this way, the heating pattern can be manipulated to provide longer heating times for selected combinations, thereby increasing the temperature of the targeted tissue. The electrodes could also be made operational in a monopolar fashion, such that an electrode (i.e., 1515 or 1501) would be active for a period of time and then another electrode would be switched on. Another embodiment would be to connect any combination of one, two, three or four electrodes to active and the return would be remote on the patient. Any of these combinations could also be multiplexed in time or have greater or lesser voltages to create more or less heating, respectively.

In some embodiments, the plurality of active electrodes are axially segmented along the axis of the shaft. Now referring to FIG. 15 b, there is provided a side view of a preferred active electrode configuration of the present invention. In this configuration, there is provided axially alternating active electrodes 1521, 1523 between insulating elements 1525, 1527 and 1529.These elements could be activated by connecting 1521 to active and 1523 to return, of the generator means. If 1521 was of a larger surface area than 1523, more heating will occur around the small surface area electrode. In a monopolar setup, the electrodes could be operated separately whether by multiplexing each in time or by applying the same or different voltages to each electrode.

In one configuration, each individual electrode terminal in the electrode array is electrically insulated from all other electrode terminals in the array within the shaft, and is connected to a power source that is isolated from each of the other electrode terminals in the array or to circuitry that limits or interrupts current flow to the electrode terminal when a low resistivity material (e.g., blood) causes a lower impedance path between the return electrode and the individual electrode terminal. The isolated power sources for each individual electrode terminal may constitute separate power supply circuits having internal impedance characteristics that act to limit the supply of power to the associated electrode terminal when a low impedance return path is encountered. By way of example, the isolated power source may be a user-selectable constant current source. In this embodiment, lower impedance paths will automatically result in lower resistive heating levels since the heating is proportional to the square of the operating current times the impedance. Alternatively, a single power source may be connected to each of the electrode terminals through independently actuatable switches, or by independent current limiting elements, such as inductors, capacitors, resistors and/or combinations thereof. The current limiting elements may be provided in the shaft, connectors, cable, controller or along the conductive path from the controller to the distal tip of the device. Alternatively, resistance and/or capacitance may be provided on the surface of the active electrode terminal(s) by providing an oxide layer that forms selected electrode terminals (e.g., titanium or a resistive coating on the surface of metal, such as platinum).

In a preferred aspect of the invention, the active electrode comprises an electrode array having a plurality of electrically isolated electrode terminals disposed over a contact surface (which may be a planar or non-planar surface, and which may be located at the distal tip of the device or over a lateral surface of the shaft, or over both the tip and lateral surface(s)). The electrode array will include at least two and preferably more electrode terminals, and may further comprise a temperature sensor. In a preferred aspect, each electrode terminal will be connected to the proximal connector by an electrically isolated conductor disposed within the shaft. The conductors permit independent electrical coupling of the electrode terminals to a high frequency power supply and control system with optional temperature monitoring of the operation of the probe. The control system preferably incorporates active and/or passive current limiting structures, which are designed to limit current flow when the associated electrode terminal is in contact with a low resistance return path back to the return electrode.

The use of such electrode arrays in electrosurgical procedures is particularly advantageous as it has been found to limit the depth of tissue necrosis without substantially reducing power delivery. Since the shaft is hollow, a conductive fluid could be added through the annulus of the shaft and flow into the bone structure for the purposes of lowering the electrical impedance and filling the spaces in the cancellous bone to make the target tissue a better conductor.

Another characteristic of conventional thermal-therapy electrode devices is the dimensionally-fixed nature of the electrode. Because of this fixed nature, the electrode can not be moved relative to the shaft, and so can not provide spatially-changing therapy unless the shaft is moved as well. Because it is often problematic to move the shaft, the fixed nature of the electrode limits the extent of thermal therapy.

Now referring to FIG. 16, in one aspect of the present invention, there is provided a thermal therapy device 1601 having a sliding electrode. In one embodiment, the shaft 1602 comprises first 1603 and second 1605 elongate portions having a reduced diameter. These reduced diameter portions are separated by an intermediate shaft portion 1607 of the shaft having a larger diameter. First 1611 and second 1613 annular electrodes has bores dimensioned so as to be slidable within those reduced diameter sections so that when the electrodes are placed upon the reduced diameter sections, slidable movement within those reduced diameter sections is obtained. Because the electrode is slidable, the electrodes may be moved to different axial locations, thereby providing the clinician with the ability to easily change the heating pattern at any selected axial location.

In some embodiments, each of the sliding electrodes is moved towards intermediate portion 1607. This results in a smaller gap between the electrodes and consequently a more compact heating pattern.

In some embodiments, each of the sliding electrodes is moved away from intermediate portion 1607. This results in a larger gap between the electrodes and consequently a more elongated heating pattern. If the gap is sufficiently large, then the heating pattern may form two essentially separate zones adjacent to the electrodes.

In some embodiments, each of the sliding electrodes is moved in the same direction (i.e., distally). This results in a more distal heating pattern.

Therefore, in accordance with the present invention, there is provided a thermal therapy device comprising:

-   a) a shaft having:     -   i) an first outer surface having first and second portions         having a first diameter, and     -   ii) a first reduced diameter outer surface located between the         first and second portions having the first diameter, -   b) a first annular electrode disposed on the reduced diameter outer     surface of the shaft and dimensioned so as to be slidable upon the     reduced diameter outer surface, the electrode being in electrical     connection with a power supply.

Also in accordance with the present invention, there is provided a thermal therapy device comprising:

-   a) a shaft having:     -   i) an first outer surface having first, second and third         portions having a first diameter, and     -   ii) first and second reduced diameter outer surface portions,         the first being located between the first and second portions         having the first diameter, and the second being located between         the second and third portions having the first diameter, -   b) a first and second annular electrodes disposed on the reduced     diameter outer surface of the shaft and dimensioned so as to be     slidable upon the respective first and second reduced diameter outer     surfaces, each electrode being in electrical connection with a power     supply so as to form and active and return electrode.

It should be clearly understood that the invention is not limited to electrically isolated electrode terminals, or even to a plurality of electrode terminals. For example, an array of active electrode terminals may be connected to a single lead that extends through the shaft to a power source of high frequency current. Alternatively, the device may incorporate a single electrode extending directly through the shaft or connected to a single lead that extends to the power source. The active electrode(s) may have a shape selected from the group consisting of a ball shape, a twizzle shapes, a spring shape, a twisted metal shape, a cone shape, an annular shape and a solid tube shape. Alternatively, the electrode(s) may comprise a plurality of filaments, rigid or flexible brush electrode(s), side-effect brush electrode(s) on a lateral surface of the shaft, coiled electrode(s) or the like.

The current applied between the return electrode(s) and the electrode terminal(s) is preferably a high or radio frequency current, typically between about 50 kHz and 20 MHz, usually being between about 100 kHz and 2.5 MHz, preferably being between about 400 kHz and 1000 kHz, often less than 600 kHz, and often between about 500 kHz and 600 kHz. The RMS (root mean square) voltage applied will usually be in the range from about 5 volts to 1000 volts, preferably being in the range from about 10 volts to 200 volts, often between about 20 to 100 volts depending on the electrode terminal size, the operating frequency and the operation mode of the particular procedure. Lower peak-to-peak voltages are preferred for thermal heating of tissue, and will typically be in the range from 100 to 1500, preferably 45 to 1000 and more preferably 45 to 80 volts rms. As discussed above, the voltage is usually delivered continuously with a sufficiently high frequency RF current (e.g., on the order of 50 kHz to 20 MHz) as compared with e.g., lasers that produce small depths of necrosis and are generally pulsed about 10 to 20 Hz. In addition, the sine wave duty cycle (i.e., cumulative time in any one-second interval that energy is applied) is preferably on the order of about 100% for the present invention, as compared with pulsed lasers which typically have a duty cycle of about 0.0001%.

The power source allows the user to select the power level according to the specific requirements of a particular procedure. The preferred power source of the present invention delivers a high frequency current selectable to generate average power levels ranging from several milliwatts to tens of watts per electrode, depending on the volume of target tissue being heated, and/or the maximum allowed temperature selected for the device tip.

The power source may be current limited or otherwise controlled so that undesired heating of the target tissue or surrounding (non-target) tissue does not occur. In one embodiment of the present invention, current limiting inductors are placed in series with each independent electrode terminal, where the inductance of the inductor is in the range of 10 uH to 50,000 uH, depending on the electrical properties of the target tissue, the desired tissue heating rate and the operating frequency. Alternatively, capacitor-inductor (LC) circuit structures may be employed, as described previously in U.S. Pat. No. 5,697,909. Additionally, current limiting resistors may be selected. Preferably, microprocessors are employed to monitor the measured current and control the output to limit the current.

The area of the tissue treatment surface can vary widely, and the tissue treatment surface can assume a variety of geometries, with particular areas and geometries being selected for specific applications. The geometries can be planar, concave, convex, hemispherical, conical, linear “in-line” array or virtually any other regular or irregular shape. Most commonly, at least one of the active electrode(s) or electrode terminal(s) will be formed at the distal tip of the device, and is frequently planar, disk-shaped, or hemispherical. Alternatively or additionally, the active electrode(s) may be formed on lateral surfaces of the electrosurgical instrument shaft (e.g., in the manner of a spatula), facilitating access to certain body structures in endoscopic procedures.

The devices of the present invention may be suitably used for insertion into any hard or soft tissue in the human body, but are most advantageously used in hard tissue. In some embodiments, the hard tissue is bone. In other embodiments, the hard tissue is cartilage. In preferred embodiments when bone is selected as the tissue of choice, the bone is a vertebral body. Preferably, the present invention is adapted to puncture the hard cortical shell of the bone and penetrate at least a portion of the underlying cancellous bone. In some embodiments, the probe advances into the bone to a distance of at least ⅓ of the cross-section of the bone defined by the advance of the probe.

In some embodiments, there is provided a preferred procedure comprising a first step of penetrating the hard cortical bone with a sharp tipped biopsy needle housed in a cannula, and a second second step of delivering a device of the present invention having a radiused or bullet nose through the cannula through the location of pierced bone.

In some embodiments, the present invention is practiced in vertebral bodies substantially free of tumors. In others, the present invention is practiced in vertebral bodies having tumors.

In some embodiments, the target region of the basivertebal nerve (BVN) is located within the cancellous portion of the bone (i.e., to the interior of the outer cortical bone region), and proximal to the junction of the BVN having a plurality of branches. Treatment in this region is advantageous because only a single portion of the BVN need be effectively treated to denervate the entire system. In contrast, treatment of the BVN in locations more downstream than the junction require the denervation of each branch.

In another embodiment, as in FIG. 17, the electrical connections between the device and the power supply can be configured so as to cause each of the tip and the shaft to become return electrodes that sandwich an active electrode.

In some embodiments of the present invention, the insulation and/or electrode geometries are selected to provide a more directional flow of current out of the device. In some embodiments, the electrode portions and insulating portions of the device are configured so that current flows through a hemi-cylindrical portion of a transverse cross-section of the device. For example, in some embodiments, as shown in FIGS. 18 a and 18 b, there is provided a device comprising a shaft 1801, a spacer 1803, and a tip 1805. The electrode portions 1807, 1809 and insulation portions 1811 of the device are configured so that current flows only across a first side 1813_of the device.

Although the embodiment shown in FIGS. 18 a and 18 b describes an active electrode surface of about 180°, other variations in the arc circumscribed by the active electrode surface are also contemplated (such as about 90°, about 270°).

In other embodiments, the active electrode surface area may change along the longitudinal axis, thereby varying the heating profile. For example, the active electrode surface may taper from a proximal 180° arc to a distal 90° arc.

In some embodiments, there is provided a device having a telescoping deployment of the electrodes. Now referring to FIG. 19 a and 19 b, there is provided a device of the present invention having insulating portions 1901 and electrodes 1903, wherein the distal tip 1905 and the electrodes 1903 are mounted on an inner shaft 1907 contained within a hollow outer hollow shaft 1909 in a concentric telescoping manner, such that the distal tip and the electrodes of the inner shaft are deployable from the hollow outer shaft. FIG. 19 a presents the device in an undeployed configuration, while FIG. 19 b presents the device in a deployed configuration. In this embodiment, an electrode 1903 is located on the distal tip 1905 of the inner shaft.

In some embodiments, the hollow outer shaft contains one or more electrodes 1904 located on or near the distal end 1911 of the hollow outer shaft.

In some embodiments, deployment of the electrodes is carried out by a simple sliding motion.

In others, the inner portion of the outer shaft and the outer portion of the inner shaft comprise complementary threadforms, so that the relative rotation of one of the shafts causes linear distal displacement of the inner shaft. The mechanical advantage provided by this embodiment provides the clinician with an increased force and increased precision.

In another embodiment, the inner portion of the outer shaft and the outer portion of the inner shaft form a complementary pin-and-helical groove structure. This embodiment allows for a more rapid deployment of the electrodes to a fixed distal position.

Deployment mechanisms for these embodiments are well known in the art and are preferably located in part upon the proximal portion of a handle of the device.

This telescoping embodiment advantageously provides the surgeon with an ability to adjust the location of an electrodes without moving the entire probe. That is, the surgeon may treat a first location, adjust the location of the electrode by telescoping, and then treat a second location.

Therefore, in accordance with the present invention, there is provided a thermal therapy device comprising:

-   -   a) an outer shaft 1909 having i) a hollow bore 1921 defining an         inner surface 1923 and an distal opening 1925, and ii) a first         electrode 1904;     -   b) an inner shaft 1907 having i) an outer surface 1927         dimensioned so as to be axially movable within the bore of the         outer shaft and across the distal opening of the outer shaft,         and ii) a second electrode 1903,         wherein the first and second electrodes are in electrical         connection with a power supply to provide a voltage         therebetween.

EXAMPLE I

This prophetic example describes a preferred dual probe embodiment of the present invention.

First, after induction of an appropriate amount of a local anesthesia, the human patient is placed in a prone position on the table. The C-arm of an X-ray apparatus is positioned so that the X-rays are perpendicular to the axis of the spine. This positioning provides a lateral view of the vertebral body, thereby allowing the surgeon to view the access of the apparatus into the vertebral body.

Next, the device of the present invention is inserted into the skin at a lateral location so that its distal tip passes posterior to the dorsal nerves located outside the vertebral body.

Next, the device is advanced interiorly into the vertebral body so that the distal tip bores through the skin, into and through the cortical shell of the vertebral body. The device is advanced until the tip reaches the anterior-posterior midline of the vertebral body.

Next, the power supply is activated to provide a voltage between the active and return electrodes. The amount of voltage across the electrodes is sufficient to produce an electric current between the active and return electrodes. This current provides resistive heating of the tissue disposed between the electrodes in an amount sufficient to raise the temperature of the local portion of the basivertebral nerve (BVN) to at least 45° C., thereby denervating the BVN. 

1. An electrosurgical device, comprising: a) a hollow shaft made of an electrically conductive material having an annular wall having a longitudinal bore therein, a proximal portion and a distal portion, and a first window extending transversely through the annular wall and defining an inside rim, and b) a first electrode disposed within the window and being in electrical connection with a power supply, and c) an electrically insulating material disposed between and contacting the entire inside rim of the first window and the first electrode to electrically isolate the first electrode from the inside rim of the window.
 2. The device of claim 1 further comprising: d) a distal tip mechanically connected to the distal portion of the hollow shaft and having a distal end adapted for piercing cortical bone.
 3. The device of claim 2 wherein the distal tip is directly joined to the distal portion of the hollow shaft.
 4. The device of claim 2 further comprising: e) an insulating spacer having a proximal end mechanically joined to the distal end portion of the hollow shaft, and a distal end mechanically joined to the distal tip.
 5. An electrosurgical device, comprising: a) a hollow shaft having an annular wall having a longitudinal bore therein, a proximal portion and a distal portion, and a first window extending transversely through the annular wall and having an inside rim, and b) an active electrode disposed within the window and being in electrical connection with a power supply, and c) a return electrode disposed within the window and being in electrical connection with the power supply, and d) an electrically insulating material disposed between and contacting the entire inside rim of the first window and the electrodes to electrically isolate the electrodes from the inside rim of the window.
 6. The device of claim 5 further comprising: e) a distal tip mechanically connected to the distal portion of the hollow shaft and having a distal end adapted for piercing cortical bone.
 7. The device of claim 6 wherein the distal tip is directly joined to the distal portion of the hollow shaft.
 8. The device of claim 6 further comprising: e) an insulating spacer having a proximal end mechanically joined to the distal end portion of the hollow shaft, and a distal end mechanically joined to the distal tip.
 9. The device of claim 5 further comprising: d) a second window disposed opposite the first window.
 10. The device if claim 5 further comprising: d) a thermocouple located within the first window.
 11. The device of claim 5 wherein each electrode is made of a material selected from the group consisting of a metal and a conductive polymer.
 12. The device of claim 5 wherein each electrode is made of a material selected from the group consisting of stainless steel, platinum, gold, copper, platinum.
 13. The device of claim 5 wherein each electrode is made of a material selected from the group consisting of a carbon-filled epoxy and a silver-filled epoxy. 